One of the main problems encountered in antibiotic production using Streptomyces is to maintain aerobic conditions in the cell culture by keeping an adequate oxygen transfer to the fermentor. A novel approach to improving oxygen availability in aerobic cultures is to introduce in the host cells genes capable of producing proteins which can modify cell metabolism to utilize the available oxygen more efficiently. In this work, Vitreoscilla hemoglobin will be expressed in a strain of Streptomyces rimosus which produces the commercial antibiotic oxytetracycline (OTC). Since OTC producers are highly sensitive to dissolved oxygen concentration, the application of the hemoglobin technology to OTC production has potential for major benefits. Functional Vitreoscilla hemoglobin will be expressed in a strain of S. rimosus which had previously been used in commercial production of OTC. The hemoglobin gene will be cloned and expressed in S. rimosus using different copy-number plasmids. The influence of hemoglobin on cell growth, oxygen consumption, and OTC production will be examined in shake flask and small- scale fermentation (2 L). Because of the extremely large and competitive market for antibiotics and other secondary metabolites synthesized by Streptomyces, this technology, which has the potential to improve productivity and final titers of product, can make a significant impact.